Voltage and Resistance Lesson Objectives: - Explain the difference between series and parallel circuits - Explain shared charge and electricity path - Explain how parallel circuits are used in the world around you. Warm up: - What do we mean when we say “resistance” in physics. Circuits Before we can discuss about the different circuits, we must first get familiar with the symbols used in electrical circuits. Circuits There are two types of circuit we can make, called series and parallel. The components in a circuit are joined by wires. If there are no branches then it's a series circuit. If there are branches it's a parallel circuit. Cell Wire Lightbulb As you can see electricity here has only one path. This is a series circuit. Circuits If you put more lamps into a series circuit, the lamps will be dimmer than before. In a series circuit, if a lamp breaks or a component is disconnected, the circuit is broken and all the components stop working. Parallel Circuits In parallel circuits different components are connected on different branches of the wire. In a parallel circuit, if a lamp breaks or a component is disconnected from one parallel wire, the components on different branches keep working. And, unlike a series circuit, the lamps stay bright if you add more lamps in parallel. Resistors in Circuits When resistors are connected in series, the current through each resistor is the same. When resistors are connected in series, the total voltage (or potential difference) across all the resistors is equal to the sum of the voltages across each resistor. In other words, the voltages around the circuit add up to the voltage of the supply. The total resistance of a number of resistors in series is equal to the sum of all the individual resistances. In this circuit the following applies. Current I1 = I2 = I3 Voltage VT = V1 + V2 + V3 Resistance RT = R1 + R2 + R3 Resistors in Parallel Circuits When resistors are connected in parallel, the supply current is equal to the sum of the currents through each resistor. The currents in the branches of a parallel circuit add up to the supply current. When resistors are connected in parallel, they have the same potential difference across them. Any components in parallel have the same potential difference across them. In order to calculate the total resistance of two resistors connected in parallel, this equation is used. Question Circuits Parallel circuits are useful if you want components to continue to work, even if one component has failed. This is why our homes are wired up with parallel circuits. Do you think Christmas trees are set up in a series or parallel circuit? Questions Current in Series Circuits The current in a series circuit is the same at all places in the circuit. Voltage in Series Circuits ● ● ● The overall voltage is shared between components in a series circuit. The sum of the voltages across components in series is equal to the voltage of the supply. The voltages across each of the components in series is in the same proportion as their resistances. This means that if two identical components are connected in series, the supply voltage divides equally across them. Current in a Parallel Circuit The current in a parallel circuit splits into different branches then combines again before it goes back into the supply. When the current splits, the current in each branch after the split adds up to the same as the current just before the split. Voltage in Parallel Circuits The voltage across components in parallel is the same for each component.
